\begin{tikzpicture}[>=Stealth, scale=0.8]
    \draw [->] (-1, 0) -- (3, 0) node[anchor=west] {$x$};
    \draw [->] (0, -1) -- (0, 3.5) node[anchor=east] {$y$};
    \node [font=\footnotesize] at (-0.3, -0.3) {$O$};

    \coordinate (Z) at (1.3, 2.6);
    \draw [dashed]
        let
            \p1 = (Z)
        in
            (\x1, 0) -- (\p1) -- (0, \y1);
    \filldraw [fill=white] (Z) circle (0.05);
    \node at ($(Z) + (0.8, 0.3)$) {$Z: a + bi$};
    \node at (0.8, -0.3) {$a$};
    \node at (-0.3, 1.3) {$b$};
\end{tikzpicture}
